1. Technical Field
The present invention relates to a robotic device, and a method of controlling a robotic device.
2. Related Art
A robotic device having a multijoint structure often used as a part of an IC handler or an assembling device has been in heavy usage in a variety of workplaces. Therefore, how fast and accurately the robotic device can move the arm to a desired position has been a performance specification and a quality of increasing significance for the robotic device.
In general, in order for moving the arm of the robotic device fast and accurately, it is preferable to reduce the inertial force acting on the arm to thereby prevent the load on the actuator for driving the arm from increasing. As one of the measures for reducing the inertial force acting on the arm, reduction in weight of the arm itself is used as an easy and effective measure. However, the reduction in weight of the arm results in degradation in the rigidity of the arm, and increases the generation of the vibration due to the deflection of the arm occurring when the arm stops. Therefore, if the tip portion of the arm is controlled to stop at a desired position, the displacement corresponding to the amplitude of the arm vibration is caused, and further, the damping time of the vibration is required as the waiting time until the subsequent action starts, which stands in the way of a high-speed operation.
In order for coping with this problem, there have been disclosed, for example, a method of disposing an acceleration sensor at the tip of the arm to operate the arm based on the acceleration signal, thus suppressing the vibration (e.g., JP-A-1-173116 (Document 1)), a method of disposing an angular velocity sensor at the tip of the arm and the arm itself to thereby controlling the arm operation based on the angular velocity signal (e.g., JP-A-2005-242794 (Document 2)), and a method of driving a driving body based on a signal of the inertial sensor disposed at the tip of the arm (e.g., JP-A-7-9374 (Document 3)).
However, in these related art documents, when the inertial sensor itself such as the acceleration sensor or the angular velocity sensor used as the standard of the arm control is at fault, even if the data signal obtained is faulty, the control based on the faulty signal is performed, which results in occurrence of danger due to runaway or the like of the robotic device. As a technology for detecting the failure of the sensor itself, it has been disclosed to previously set a threshold value with respect to the detection value of the sensor, and to determine that the sensor is at fault when the difference between the threshold value and the detected value exceeds a judgment value (JP-A-2009-8412 (Document 4), JP-A-2009-184035 (Document 5)).
However, according to the technology disclosed in the documents mentioned above, since the threshold value is previously set based on the detection value obtained when the sensor to be used operates normally, the detected value might fail to exceed the threshold value in a variety of actual operation states of the robotic device even if the sensor is at fault, which might fail to perform the accurate failure determination.